An analog arithmetic circuit in which analog data input from an input device is used for arithmetic processing can output an analog value as data obtained by the arithmetic processing. Therefore, data does not have to be converted into digital data, and thus, a DA converter circuit or the like, which is necessary for data conversion from an analog value into a digital value, is unnecessary. Moreover, an analog arithmetic circuit is considered to have an advantage of low power consumption because its capability of large-scale real-time data processing enables a reduction in power for data transfer.
The following Patent Document 1 discloses a liquid crystal display device in which, as compared with arithmetic operation with digital data, low-power and short-time arithmetic operation is achieved by an analog arithmetic circuit utilizing voltage-current characteristics of MOS transistors. In addition, the following Patent Document 2 discloses an analog-digital mixed arithmetic circuit including a plurality of analog arithmetic circuits, a capacitor which accumulates the sum of arithmetic operation results as the amount of charge, a comparator which converts the amount of charge into a corresponding pulse signal, a pulse width-digital conversion circuit which converts the pulse signal into a digital signal, and a digital arithmetic circuit which calculates the cumulative value in accordance with the digital signal.